Want to calculate someone's age? Cool, try this age calculator.

This age calculator determines someone's (or something's) age in the following formats:

- Years + Months + Days
- Months + Days
- Weeks + Days
- Days
- Hours
- Minutes
- Seconds

Calculating an age in terms of months plus days can be straightforward, or somewhat tricky, depending on the circumstances. For example, we can probably all agree that a baby born on January 1st, 2000, will be one month old on February 1st, 2000, that's easy. But now consider a baby born on January 31st, 2000. On what date will that baby be one month old? Well, according to Merriam-Webster's Dictionary a month is:

*"The period from a day of one month to the corresponding day of the next month if such exists or if not to the last day of the next month (as from January 3 to February 3 or from January 31 to February 29)."*

So, that means that a baby born on January 31st, 2000, will be one month old on the last day of the next month (February). Since the year 2000 is a leap year, there are 29 days in February, so a baby born on January 31st will be one month old on February 29th.

What's interesting, however, is that a baby born on January 30th, 2000, will ALSO turn one month old on February 29th, 2000. And, a baby born on January 29th, 2000, will ALSO turn one month old on February 29th, 2000. So we can have a situation where three different babies, all born on different days (January 29th, 30th, and 31st) all turn one month old on the same day (February 29th). In terms of days they are all different ages, but in terms of months they are all exactly one month old!

This calculator uses the Merriam-Webster definition above when calculating age in months.

Most people know that leap years occur on years that are evenly divisible by four, but did you know that some years that are evenly divisible by four are actually not leap years? That's right. If a a year is evenly divisible by four, but also evenly divisible by 100, then it is only a leap year if it also evenly divisible by 400. This means that the year 2000 was a leap year (because it's evenly divisible by four, 100, and 400), but the year 2100 will not be a leap year (because it's evenly divisible by four and 100, but not 400).

Anyway, this calculator knows how to figure out what years are and are not leap years, so rest assured that ages determined in days are exact, and account for each and every leap day that has happened between the "Date of Birth" and "Age On" dates.

If you want to work with years from the BC (Before Christ) time period, also known as BCE (Before Common/Current Era), simply put a minus sign in front of the year.